Arc protected high frequency electron discharge devices and waveguide window coupling assembly



3,345,535 EVICES NSON Louas T. ZITELLI FNVENTURS HARGE D FLOYD 0. JOH

u Qm 8Q 6538. W t2 0 2 1957 F. o. JOHNSON ETAL ARC PROTECTED HIGH FREQUENCY ELECTRON DISC AND WAVEGUIDE WINDOW COUPLING ASSEMBLY Filed Aug. 26, 1964 Patented Oct. 3, 1967 3,345,535 ARC PROTECTED HIGH FREQUENCY ELECTRON DISCHARGE DEVICES AND WAVEGUIDE WIN- DOW COUPLING ASSEMBLY Floyd 0. Johnson, Mountain View, and Louis Thomas Zitelii, Palo Alto, Calif, assignors to Varian Associates, Palo Alto, Calif., a corporation of California Filed Aug. 26, 1964, Ser. No. 392,211 7 Claims. (Cl. 315-39) This invention relates in general to the field of high frequencyelectron discharge devices preferably operable in the microwave spectrum, and more particularly to such devices having improved electromagnetic wave permeable waveguide window coupling means incorporated therein.

Designers of high frequency microwave power sources such as, for example, klystrons, traveling wave tubes, magnetrons, etc., are constantly plagued by tube failures resulting from environmental causes over which they have no control. A tube designer may build a perfect tube and ship it to a customer for utilization in a specific system such as, for example, radar applications, troposcatter communications, etc., and the tube will function per design characteristics and then failure will occur due to defects in the system itself and/or carelessness by the systems people in working the particular tube under consideration into the system as an integral part thereof. For example, a technician may be installing a high power microwave klystron amplifier or traveling wave tube in an antenna system and when hooking the amplifier into the waveguide coupled to the antenna, it is quite conceivable and in fact has happened, that some abnormal obstruct-ion, such as for example, a wrench, screw driver, etc., is accidentally left inthe interconnecting waveguide system with the result that upon commencing of operation a high power are will result from the obstruction, which are will then travel toward the power source with the result, in not a few instances, in window failure for the elecromagnetic vacuum sealed wave permeable window portion of the tube. This,--of course, could result in total effective destruction' of the tube itself, due to the air and/ or gas leakage therein through the window.

. Other causes of high power arcs in interconnecting waveguide systems are askewed waveguide flanges which result in physical perturbations in the interconnecting waveguide system, moisture, water, dirt seepage in the interconnecting waveguide system, etc. In each instance the physical perturbation existing in the interconnecting waveguide system can and does result, due to the impedance discontinuity of said perturbations, in the generation of a high power are which can and does travel toward the power source with the resultant destruction of the vacuum sealed electromagnetic wave permeable window.

The present invention obviates such window failures with the utilization of a novel are protective additional electromagnetic wave permeable window in conjunction with the vacuum sealed window which is conventionally 'a part of the microwave amplifier. The present invention furthermore results, through the utilization of selective relative positioning of the arc protective window with respect to the vacuum window, in an enhanced bandwidth characteristic for the window combination without, the incorporation of additional broadbanding perturbations in the waveguide system.

The present invention through the utilization of a selfresonant block window in conjunction with another selfresonant block window, said windows being spaced relative to one another within specified limits, results in the obtaining of a matched relatively broadbanded substantially refiectionless electromagnetic wave permeable waveguide window coupling assembly having improved bandwidth characteristics over the operating frequency range thereof in comparison to a single self-resonant block type of waveguide window coupler assembly as taught by the prior art. The present invention obviates the necessity of incorporating matching irises of the lumped or distributed parameter variety or impedance discontinuities as heretofore utilized in broadbanding self-resonant windows with a resultant increased ability to handle high powers without danger of breakdown occurring as heretofore existed in broadbanded systems utilizing auxiliary lumped or distributed broadbanding elements.

It is therefore an object of this invention to provide an improved high frequency electron discharge device preferably operable in the microwave spectrum.

A feature of the present invention is the provision of a high frequency electron discharge device having an improved electromagnetic wave permeable waveguide window coupler assembly attached thereto.

Another feature of the present invention is the provision of a high frequency electromagnetic wave permeable waveguide window coupling assembly incorporating a pair of spaced self-resonant windows adapted and arranged to be attached to an electron discharge device and designed such as to have a broader passband than an individual self-resonant window per se.

Another feature of the present invention is the provision of a high frequency electron discharge device having a wave permeable vacuum sealed window incorporated as an integral part thereof and including another self-resonant window fixedly, yet removedly, coupled to said selfresonant vacuum sealed window such as to function as an arc protective means for said device.

Another feature of the present invention is the provision of a high frequency electromagnetic wave permeable waveguide window coupler assembly which incorporates a pair of self-resonant windows, said windows each being designed to be self-resonant within the resultant passband of said coupler and wherein said windows are spaced from each other as measured along the direction of electromagnetic wave energy transmission through said windows withinthe following limits:

wherein s=the spacing between opposed faces of said windows, n=any positive integer, and A equals guide wavelength as determined at the self-resonant frequency of at least one of said windows.

These and other features of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view, partly sectioned of a high frequency electron discharge device of the klystron type having a novel waveguide window coupler assembly attached thereto as taught by the present invention;

FIG. 2 is an elevational view taken along line 22 of FIG. 1 showing the relative dimensions of the input and output guides;

FIG. 3 is an enlarged cross-sectional view, taken along line 3-3 of FIG. 1 showing the coupler portion of FIG. 1;

FIG. 4 is an illustrative graphical portrayal of band width characteristics for various self-resonant block windows depicting VSWR vs. frequency characteristics thereof as taught by the present invention;

FIG. 5 is an illustrative graphical portrayal of the effect of varying the spacing(s) between a pair of self' resonant block windows as taught by the present inven tion.

The klystron 7, depicted in FIG. 1 is. merely an illustrative example of high frequency electron discharge devices which are advantageously benefitted by incorporation of the particular are protective broadbanded waveguide window coupler design of the present invention.

Reference to any of numerous reference texts, technical articles, etc., may be made for particular details of constructional techniques utilized in building high frequency electron discharge devices such as typified by the klystron set forth in FIG. 1. For example, reference to US. patent application Ser. No. 148,520 by L. T. Zitelli et al., filed Oct. 30, 1961 and assigned to the same assignee as the present invention, will provide a description of a klystron of the type depicted in FIG. 1.

Briefly, the klystron depicted in FIG. 1 includes at the upstream end thereof, a beam forming and projecting means 8 coupled via the intermediary plurality of resonant cavities surrounded by the main body portion 9 to a beam collecting region 10 disposed at the downstream end thereof. The typical tuner mechanism assemblage 11 is utilized to tune each of the resonant cavities disposed in the main body portion 9 to a desired frequency according to conventional design practice.

Microwave electromagnetic energy to be amplified is introduced into the input cavity disposed in the main body portion 9 by being coupled from a source point (not shown) through coupling waveguide section 12 through electromagnetic wave permeable vacuum sealed window assembly 13 which is preferably of the type shown in US. Patent No. 2,958,834 by R. Symons et al., assigned to the same assignee as the present invention, and thence through intermediate waveguide coupling section 14 from where the energy is coupled into the input cavity where it will be amplified per conventional practice. The amplified electromagnetic wave energy is extracted from the klystron 7 through output waveguide 15 from whence it may be directed to any suitable load device as an antenna (not shown). Waveguide 15 has an electromagnetic wave energy transmission waveguide window coupler portion which includes a self-resonant block window 16, vacuum sealed therein by any conventional technique. A waveguide flange 17 is preferably fixedly secured to the end portion 18 of the waveguide, as shown. Coupled to the flange 17 is auxiliary flange member 19 which contains therein another self-resonant block window 20 which can be vacuum sealed using conventional techniques within the rectangular guide portion of flange member 19. A flange member having rectangular guide portion 21 provides a rigid mechanical tie between the input and output guides. The waveguide and flange portions previously described are advantageously made of such high conductivity material as electrolytic copper, such as the OFHC type and the block windows are advantageously made of any conventional low loss dielectric materials such as alumina (A1 300), beryllia (BeO), single crystal sapphire, etc.

Block window 16 is designed per conventional practice to be self-resonant (reflection coeflicient=0 or expressed another way /zk thick where A =waveguide wavelength of the dielectric window portion) at any fre quency within the resultant passband of the waveguide window coupler assembly although preferably at for maximum bandwidth where f is the center frequency of the passband of the waveguide window coupler assembly or the center frequency of the operating band of the tube. Arc protective or auxiliary window 20 is similarly designed to be self-resonant in the same manner as block window 16 and preferably at the same frequency as block 16. Window 20 may advantageously be brazed within the flange member 19 in a vacuum sealed manner and the region 22 between the two block windows may advantageously be evacuated through use of any suitable tubulation, etc., per conventional practice to a vacuum equivalent to the tube vacuum or at a higher pressure, according to the teachings of the present invention. Furthermore, any conventional low loss cooling fluid may be passed between the windows to enhance the power handling capacity of the combination. It is noted that there are no auxiliary protuberances such as capacitive or inductive irises in the waveguide 15 utilized to enhance the broadband characteristics of the coupler assembly. Quite obviously, any of the know broadbanding techniques utilizing distributed or lumped capacitive and/or inductive irises may be incorporated within the coupler assembly to further increase the bandwidth thereof, beyond the teachings of the present invention.

It has been determined and is taught by the present invention that spacing(s) between the opposed face portions 23, 24 as taken along the direction of energy propagation Z between the two block windows 16 and 20 when falling within specified limits as set forth hereinafter will provide an improved bandwidth characteristic for the coupler assembly in comparison with that obtainable with a single self-resonant block as taught by the prior art.

The are protective self-resonant block 20 may also, according to the teachings of the present invention, be incorporated in and as an integral part of the output waveguide 15 rather than be positioned in an auxiliary removable flange 19 as shown in FIG. 3. Furthermore, the coupler assembly may be sold as an integral unit and attached to any conventional klystron, magnetron, etc., as a separate arc-protective scheme. This, of course, means that both block windows can be vacuum sealed within the surrounding guide or not as a matter of design preference since the tube to which the coupler assembly is appended may or may not have its own vacuum win dow. Thus, the present invention teaches and claims the concept of a self-resonant pair of block windows particularly spaced from each other such as to provide enhanced bandwidth characteristics for the combination and are protection.

The present invention includes the concept of positioning the arc protective window within a detachable or removable flange member 19 with the arc protective window disposed therein, either under vacuum sealed or nonvacuum sealed conditions, depending on the system user preferences. It is then a simple matter when upon occurrence of an arc in the load portion of the system within which the electron discharge device is utilized which are fractures the arc protective window 20, to simply remove the flange portion and substitute another flange portion 19 having an arc protective block window 20 or pair of windows disposed therein and minimization of overall cost of replacement is obviously facilitated.

Directing your attention to FIG. 4, several characteristic bandwidth or passband curves on a VSWR vs. frequency characteristic are depicted. The passband or bandwidth is characteristically and herein defined as fhi+f1o and VSWR is 1.2 or less where f and f are determined at 1.2 VSWR. Characteristic A depicts typical bandwidth or passband of a self-resonant block window designed to be self-resonant at f the center frequency of the passband which in the graphical portrayal is 10 go. Characteristic B depicts the resultant enhanced broadbanding characteristics obtained when a pair of self-resonant blocks are spaced Mu from each other in rectangular guide. Characteristic C depicts the enhanced broadband characteristics obtained when a pair of self-resonant blocks, wherein self-resonance for each block is similar to the condition used for curve B, namely 10 gc., are spaced apart. It is to be noted that the Mih spacing provides greatly increased bandwidth characteristics in comparison to a single self-resonant block window and also that the spacing similarly provides increased bandwidth characteristics in comparison with a single self-resonant block window although not as greatly as the Ma spacing. It is also obvious that the bandwidth is, practically speaking, symmetrical about the frequency at which the blocks are designed to be self-resonant. In each of the above instances i was determined at the self-resonant frequency of the block or blocks and each block was cut to be self-resonant at the same frequency, namely 10 gc.

The bandwidth characteristics depicted in FIG. show the effects of increasing and decreasing the spacing(s) between the spaced block windows designed to be Mix apart. CharacteristicD shows the effect on the bandwidth and VSWR amplitude characteristics when the spacing is decreased 0.75 inch from A /4 wherein each of the blocks are self-resonant at, 10.0 gc. and A is determined at 10.0 gc. Characteristic E depicts the resultant effects on the bandwidth and VSWR amplitude characteristics when the spacing(s) is increased .075 inch greater than A /4, wherein A is again determined at 10.0 gc. It is obvious upon examination of FIGS. 4 and 5 that a fair amount of variation of the parameters, namely, the S parameter and the particular frequency or frequencies at which the blocks are designed to be self-resonant may be employed by tube designers without departing from the scope of the present invention.

The spacing(s) will, according to the teachings of the present invention, fall in the following limits:

wherein s is the spacing between opposed faces of the two windows determined along the direction of energy propagation in the coupler Z, and n=any positive integer, A =waveguide wavelength as determined at the selfresonant frequency of at least one of said windows. Examination of FIG. 5 shows that a deviation on a 1L basis from the A /4 spacing(s) between the two windows destroys the passband symmetry about the frequency at which the block windows are designed to be self-resonant. This effect may advantageously be employed as a means of easily controlling the particular passband for which the waveguide window coupler assembly is designed. It is to be understood that the particular guide and window configurations although described in terms of rectangular guide may advantageously be circular.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A high frequency electron discharge device including electromagnetic wave transmission waveguide window coupler means wherein said coupler means is characterized by having a pair of self-resonant electromagnetic wave permeable Windows disposed therein in spaced relationship along the direction of energy propagation through said coupler, wherein said spacing between said windows falls within the following limits:

wherein s=the spacing between opposed faces of the windows, n=any positive integer, and x =guide wavelength as determined at the self-resonant frequency of at least one of said pair of windows, each of said self-resonant windows being substantially /zk thick as determined at a frequency within the passband of said coupler means where A =waveguide wavelength of each window portion.

2. The device as defined in claim 1 wherein each of said windows are designed to be self-resonant at f where f is the center frequency of the resultant passband of said coupler means.

3. The device as defined in claim 1 wherein said coupler means includes two portions, one of said portions having one of said windows disposed therein and vacuum sealed to the defining walls of said coupler means and wherein said second portion includes the other of said windows disposed within a detachable flange member, said detachable flange member being; fixedly yet removably secured to said first portion of said coupler means.

4. A high frequency electron discharge device having an electromagnetic wave permeable self-resonant window vacuum sealed in a waveguide coupled to said device in vacuum sealed relationship therewith, said waveguide having an additional waveguide coupled thereto in a fixed yet removable relationship, said additional waveguide having another self-resonant window disposed therein in spaced relationship with respect to said vacuum sealed window, each of said windows being designed to be selfresonant within the resultant passband of said pair of windows and waveguide, each of said self-resonant windows being substantially /zx thick as determined at a frequency within the resultant passband of said waveguide-window combination, said pair of spaced selfresonant windows being spaced apart, as determined along the direction of energy transmission through said waveguide, a distance which falls within the following limits:

wherein s is the spacing between opposed faces of said windows, n=any positive integer, and A =waveguide wavelength as determined at the self-resonant frequency of at least one of said windows.

5. A high frequency electron discharge device including an output waveguide coupled thereto, said output Waveguide designed to extract high frequency electromagnetic wave energy from said device, said output waveguide having a self-resonant window vacuum sealed therein, said waveguide having a coupling flange attached to the end thereof, said flange including an aperture extending therethrough which forms an extension of said output waveguide, said aperture having a self-resonant window disposed therein, the spacing between said pair of self-resonant windows falling within the following limits:

wherein s=spacing between opposed faces of said windows, n=any positive integer, and A =waveguide wavelength as determined at the self-resonant frequency of at least one of said windows, and wherein each of said windows is designed to be self-resonant at a frequency within the operating passband of said device, each of said self-resonant windows being substantially /za thick as determined at a frequency within the resultant passband of said waveguide window combination where A =waveguide wavelength of each window portion.

6. A waveguide window coupling assembly for microwave electromagnetic energy including a waveguide having a self-resonant window disposed therein, said waveguide having another self-resonant window disposed therein in spaced relationship from said first self-resonant window, the spacing between said two windows .falling within the following limits:

wherein s=spacing between opposed faces of said windows, n=any positive integer and x =waveguide wavelength as determined at the self-resonant frequency of at least one of said windows, each of said self-resonant windows being substantially A /Z thick as determined at a frequency within the resultant passband of said waveguide window combination where h =waveguide wavelength of each window portion.

7. The assembly as defined in claim 6 wherein said windows are each designed to be self-resonant at the same frequency.

(References on following page) References Cited UNITED STATES PATENTS 2,407,911 9/1946 Tonksetal 333-33 2,834,949 5/1958 Duffy 333 9s 5 2,930,008 3/1960 Walsh 333-98 OTHER REFERENCES IRE Transactions on Microwave Theory and Techniques High Power, Magnetic Field Controlled Microwave Gas -8 Discharge Switchesby S, J. Tetenbaum and R. M. Hill, vol. MTT7, No. 1, January 1959, p. 79, TK 7800 123. 7800 123.

Microwave Transmission Circuits, Ragan, McGraw- Hill, New York, 1958, pp. 222 to 223.

ELI LIEBERMAN, Primary Examiner.

HERMAN KARL SAALBACH, Examiner.

M. NUSSBAUM. Assistant Examiner. 

1. HIGH FREQUENCY ELECTRON DISCHARGE DEVICE INCLUDING ELECTROMAGNETIC WAVE TRANSMISSION WAVEGUIDE WINDOW COUPLER MEANS WHEREIN SAID COUPLER MEANS IS CHARACTERIZED BY HAVING A PAIR OF SELF-RESONANT ELECTROMAGNETIC WAVE PERMEABLE WINDOWS DISPOSED THEREIN IN SPACED RELATIONSHIP ALONG THE DIRECTION OF ENERGY PROPAGATION THROUGH SAID COUPLER, WHEREIN SAID SPACING BETWEEN SAID WINDOWS FALLS WITHIN THE FOLLOWING LIMITS: 